If you were to take a little bit of dairy, add a slightly larger serving of vegetables, fruits and proteins, and then pile on as many superfluous oils, fats, and grains as possible, you would have a reasonably accurate depiction of the modern American diet.

Americans on average now eat nearly 2,600 calories a day, almost 500 more than they did forty years ago, according to the USDA, which uses food production data, along with spoilage and waste estimates, to approximate per capita consumption.

That increase alone should be enough to raise an eyebrow (or three hundred million), but what's most troubling isn't the increase in our caloric intake, so much as its make-up. Over 92% of the uptick in per capita caloric intake since 1970 is attributable to oils, fats, and grains. Thirty years ago, the combination was responsible for roughly 37% of our daily calories; today, it makes up closer to 47% of our diet.

What exactly we should glean from that reality isn't entirely clear. Oils, fats, and grains, aren't inherently bad. In fact, there's good reason to believe that many fats and oils are actually just the opposite. And grains, despite a growing narrative about their potential harms, come in all shapes and sizes—some are protein-rich, like quinoa, while others offer little, if any, nutritional value, such as enriched white flour.

But to call a calorie a calorie is misguided—especially if one is highly processed, or refined—and it's easy enough to extrapolate from the kind of calories we're consuming more of nowadays. It's likely of little coincidence, for instance, that the two food groups Americans are eating more and more of—added fats and oils, and flour and cereal products—are the same ones that are found in most processed and fast foods.

"It's hard to pinpoint why exactly it's increased," Jeanine Bentley, the social science analyst responsible for the USDA's food availability database, said in an interview. "But it probably comes from an increase in processed and fast foods."

Bentley isn't blindly holding her finger to the wind. A 2013 study by USDA's Economic Research Service seems to confirm her suspicion. Fast food is a much more integral part of the American diet than it was in the 1970s. Between 1977 and 1978, fast food accounted for just over 3% of calories in the US diet; between 2005 and 2008, that share skyrocketed to over 13%.

Americans are also spending almost three times the recommended amount on refined grains, and many times more than the recommended amount on frozen and refrigerated entrees, according to the same study.

The sum of all those calories, which appear to largely be the wrong kind of calories, is an ever-expanding American waistline. Americans aged 20 and older are now almost three times as likely to be obese as they were only 30 years ago—the increase is enough to afford the U.S. the unenviable distinction of being the most obese major country in the world.

That distinction is that its more than merely a health conundrum; it's a full-fledged economic problem, too. As of 2008, the annual medical costs alone of obesity amounted to almost $150 billion, according to the Center for Disease Control and Prevention. Some, including food journalist Mark Bittman, believe the total annual costs of the epidemic in the US could now exceed $1 trillion.

Roberto A. Ferdman is a reporter for Wonkblog covering food, economics, immigration and other things. He was previously a staff writer at Quartz.

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